As shown in Japanese Patent Unexamined Publication 2013-14965 (Patent Document 1) and Japanese Patent Unexamined Publication 2011-214262 (Patent Document 2), urinals comprising a discharge trap at the bottom of a bowl portion for receiving a user's urine are known.
In the urinal shown in Patent Document 1 and Patent Document 2, a discharge trap has: a downward extending descending conduit, a horizontal conduit bending gradually from the descending conduit and extending horizontally, and an ascending conduit similarly gradually bending from the horizontal conduit and extending upward; and is approximately U-shaped.
A predetermined amount of pooled water is constantly pooled at the bottom portion of the discharge trap in order to prevent the intrusion of foul odors or the like from drain pipes; a water seal is formed by the pooled water.
In the type of conventional urinal, when a user urinates urine flows into the discharge trap; the majority of pooled water is discharged by the inflow of urine, and inside the discharge trap a liquid with a high urine concentration mixture of urine and water is present as pooled water.
When flush water is supplied to the bowl portion to flush the bowl portion after use by a user, the flush water once again flows from the bowl portion into the discharge trap; high urine concentration pooled water is discharged from the discharge trap, and high urine concentration pooled water in which urine and water are mixed in the discharge trap is replaced by low urine concentration flush water newly flowing into the discharge trap.
In the past, the problem has occurred that if the substitution rate (the ratio at which pooled water pooled in the discharge trap is substituted by new flush water) is low when the high urine concentration pooled water consisting of mixed urine and water in a discharge trap is substituted by flush water with a low urine concentration newly flowing into the discharge trap, the urine concentration in the post-substitution pooled water increases, making it easier for uric scale to form.